A disturbing video posted online appears to show a militant beheading American journalist James Foley and threatening a second American captive with a similar fate.

In the video a man who appears to be Foley, dressed in orange, kneels beside an armed man clad in black. Foley delivers a statement condemning U.S. action in Iraq and says that the U.S. government is his “real killers.”

“For what will happen to me is only a result of their complacency and criminality,” Foley says in halting speech. “I wish I had more time. I wish I could have the hope of freedom of seeing my family once again, but that ship has sailed. I guess all in all, I wish I wasn’t American.”

A screengrab from a video posted online appears to show American journalist James Foley shortly before he is killed by a masked captor.

Seconds later, the figure dressed in black brandishes a knife and identifies himself as with the Islamic State, the name the brutal terror group Islamic State of Iraq and Syria took on after its leader, Abu Bakr al-Baghdadi, declared himself the leader of all Muslims.

“Today your military air force has attacked us daily… Your strikes have caused casualties amongst Muslims,” the figure in black says. He then addresses President Obama directly, saying “any attempt… to deny the Muslims their right to live in safety under the Islamic caliphate will result in the bloodshed of your people.”

Foley is then killed. The video continues, showing American Steven Sotloff, who has written for national publications like Time, also dressed in orange and on his knees.

“The life of this American citizen, Obama, depends on your next decision,” the figure in black says.

Obtained by ABC News

American Steven Sotloff is seen in a gruesome video posted online that earlier appears to show the murder of American journalist James Foley.

A spokesperson for the White House National Security Council said the U.S. intelligence community "is working as quickly as possible to determine its authenticity."

"If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends," spokesperson Caitlin Hayden wrote in a statement to reporters. The U.S. government offers a $10 million reward for information leading to ISIS leader al-Baghdadi’s capture.

A statement posted on the Free James Foley Facebook page and attributed to Foley’s mother, Diane, said his family has “never been prouder of our son Jim.”

“He gave his life trying to expose the world to suffering of the Syrian people,” the note says. “We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents... We thank Jim for all the joy he gave us. He was an extraordinary son, brother, journalist and person."

Foley was on assignment in Syria for the news outlet GlobalPost when he was kidnapped in November 2012. The news organization's co-founder Charles Sennott said today there is "no reliable proof that this execution is authentic" and that they're working to gather information.

"If the video is verified, it is just unfathomable darkness to think that a life as bright as Jim Foley's ended that way," Sennott said. "He was an experienced and fearless journalist who believed deeply in reporting from the front lines."